Supine MRI for regional breast radiotherapy: imaging axillary lymph nodes before and after sentinel-node biopsy

Tristan C F Van Heijst,Nienke Hoekstra,Debora Eschbach-Zandbergen,Jan J W Lagendijk,Thijs Van Dalen,Arjen J Witkamp,H J G Desirée Van Den Bongard,Bram Van Asselen,Stephanie N De Waard,Marielle E P Philippens,Ruud M Pijnappel,Helena M Verkooijen

doi:10.1088/1361-6560/aa759f

Abstract

Regional radiotherapy (RT) is increasingly used in breast cancer treatment. Conventionally, computed tomography (CT) is performed for RT planning. Lymph node (LN) target levels are delineated according to anatomical boundaries. Magnetic resonance imaging (MRI) could enable individual LN delineation. The purpose was to evaluate the applicability of MRI for LN detection in supine treatment position, before and after sentinel-node biopsy (SNB). Twenty-three female breast cancer patients (cTis-3N0M0) underwent 1.5 T MRI, before and after SNB, in addition to CT. Endurance for MRI was monitored. Axillary levels were delineated. LNs were identified and delineated on MRI from before and after SNB, and on CT, and compared by Wilcoxon signed-rank tests. LN locations and LN-based volumes were related to axillary delineations and associated volumes. Although postoperative effects were visible, LN numbers on postoperative MRI (median 26 LNs) were highly reproducible compared to preoperative MRI when adding excised sentinel nodes, and higher than on CT (median 11, p < 0.001). LN-based volumes were considerably smaller than respective axillary levels. Supine MRI of LNs is feasible and reproducible before and after SNB. This may lead to more accurate RT target definition compared to CT, with potentially lower toxicity. With the MRI techniques described here, initiation of novel MRI-guided RT strategies aiming at individual LNs could be possible.

Highlights

In recent years, regional treatment for breast cancer patients with tumour-positive sentinel nodes (SNs) has changed
In conventional regional breast RT, target volumes are contoured on computed tomography (CT) scans, according to contouring guidelines, including those recently published by the European Society for Radiotherapy and Oncology (ESTRO) (Offersen et al 2015)
We have previously developed dedicated Magnetic resonance imaging (MRI), in healthy volunteers, to image axillary lymph node (LN) for RT planning in supine treatment position

Summary

Introduction

Regional treatment for breast cancer patients with tumour-positive sentinel nodes (SNs) has changed. In conventional regional breast RT, target volumes are contoured on computed tomography (CT) scans, according to contouring guidelines, including those recently published by the European Society for Radiotherapy and Oncology (ESTRO) (Offersen et al 2015). These guidelines focus on the delineation of axillary levels based on vessels and muscles, since LN visibility on CT is limited. Anatomical information on exact LN locations obtained from dedicated MRI techniques may lead to adapted regional breast RT target volumes, such that more healthy tissue can be spared This could result in decreased RT-related toxicity, consisting of arm morbidity, e.g. pain, edema, and shoulder stiffness.

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